A decision on the other suspects will be taken on Monday.
The police crackdown, 13 months after four suicide bombers killed 52 people on London's transport system, has prompted a reaction from British Muslims who say that they are being demonised by the militancy of a few.
In an open letter to Tony Blair, the British prime minister, leading British Muslim groups and politicians criticised British foreign policies on Iraq and the Middle East crisis and said that these policies were putting civilians at increased risk of attack in Britain and elsewhere.
"The debacle of Iraq and now the failure to do more to secure an immediate end to attacks on civilians in the Middle East not only increases the risk to ordinary people in that region, it is also ammunition to extremists who threaten us all," they said in the letter, published in the Times newspaper.
Fuelling the fire
Many Muslims are critical of Blair's decisions to commit British troops to the 2003 US-led invasion of Iraq and not to call for an immediate halt to the fighting between Israel and Hezbollah.
"We urge the prime minister to redouble his efforts to tackle terror and extremism and change our foreign policy," said the letter, whose signatories included six politicians from Blair's Labour party.
Responding to the letter, Douglas Alexander, the British transport secretary, told Britain's Channel 4 television: "Nothing justifies the kind of actions which terrorists perpetrate."
Chaos at London airports eased on Friday as passengers became used to tight security measures such as the ban on liquids being carried on to flights from US or British airports.
British Airways warned customers to expect further flight delays and cancellations at Heathrow airport on Saturday.
Suspected terrorists have been carrying out training exercises in national parks in England and Wales, The Guardian reported on Monday, citing unnamed security sources.
According to the newspaper, undercover detectives, believed to be from London's metropolitan police anti-terrorist branch, have been monitoring groups of around 20 men, some of whom have known terrorist connections.
The suspected terrorists have been carrying out their exercises, which did not involve explosives or weapons training, in the Lake District, in northwest England, and investigators have apparently built up evidence to be passed on to government prosecutors.
The Guardian article said: "Police believe they have clear evidence that the men were preparing for a mission of some sort."
The newspaper reported that none of the suspected terrorists involved were believed to be related to Thursday's arrests of 24 suspected terror plotters, who were allegedly planning to blow up US-bound passenger jets in mid-flight.